1. Field of Invention
This invention relates to flash memories and more particularly to flash memory cells created from micro vacuum tube technology.
2. Description of Related Art
A micro vacuum tube is a cold cathode field emission device in which electrons are emitted into a vacuum at room temperature under a sufficiently high electric field. The electric field does not require a high voltage to produce emission providing that the emitting surface has a sufficiently small radius of curvature. Electrons are emitted by the cold cathode past a selector gate and collected at an anode. The anode can be a floating gate of a flash memory cell. One of the advantages of the micro vacuum tube is the small area required on the surface of a semiconductor substrate. The micro vacuum tube devices can be manufactured on the surface of a semiconductor substrate using integrated circuit techniques and finally sealing the micro vacuum tube with a layer of metalization under a vacuum.
In U.S. Pat. No. 5,731,597 (Lee et al.) a field emitter array (FEA) is incorporated with MOSFET's using common processing steps. In U.S. Pat. No. 5,651,713 (Lee et al.) describes a method for manufacture of a low voltage FEA array with minute gate holes on a semiconductor substrate. In U.S. Pat. No. 5,231,606 (Gray) is disclosed a FEA array having two or more collector electrodes, an extractor electrode, at least one deflector electrode and at least one electron field emitter.
In nonvolatile memories such as flash memories the durability of the oxide in the program and erase path is key to the longevity of the flash memory. A major issue with the development of flash memories is lessening the program and erase damage; however, it is inevitable that the oxide quality will decay and eventually end the useful life of a flash memory cell. A micro vacuum tube technology forming an FEA provides a means by which the classical degradation of an oxide does not exist because hot carriers are not used as a means to charge a floating gate. Instead a flow of electrons from a cold cathode is used to providing the charge for the floating gate.